Project Summary/Abstract The lateral preoptic area (LPO) is a hypothalamic structure whose function is largely unknown. There is evidence that stimulating the LPO elicits locomotion, and that this structure supports intracranial self- stimulation, suggesting that the LPO could be part of the ?brain reward system?. The LPO also sends strong projections to the ventral tegmental area (VTA), a key member of the brain reward circuit. This further positions the LPO as a potential member of the brain reward system and, in particular, as a modulator of VTA activity. This is significant because structures that modulate VTA activity have been shown to play a critical role in cocaine seeking; increases in VTA dopamine neuron activity trigger relapse (i.e. increase drug seeking), whereas decreases reduce seeking. It is unknown if the LPO functionally regulates the activity of VTA neurons and cocaine seeking behavior. The objective of this proposal is to understand if and how the LPO regulates the activity of VTA neurons (Aim 1) and cocaine seeking behavior (Aim 2). In addition, the proposal will examine the contribution of the LPO- VTA pathway in any observed effect, and the neurotransmitters (GABA or glutamate) involved. This will be achieved by manipulating (increasing or decreasing) the activity of the LPO and LPO-VTA pathway; this will determine if this structure and pathway are sufficient and/or necessary for regulating the activity of VTA neurons and cocaine seeking behavior. Activity will be manipulated using three approaches: pharmacology, chemogenetics, and optogenetics. The activity of VTA neurons (GABA and dopamine) will be evaluated with in vivo extracellular recordings in anesthetized rats. Cocaine seeking will be evaluated after cocaine self-administration, by examining responding in the absence of cocaine. Sucrose seeking will also be tested, to examine if the role of this structure and pathway extends to seeking for natural rewards. The neurochemical nature of the LPO-VTA pathway will be probed (i) using pharmacology, (ii) by measuring synaptic currents, and (iii) by performing immunohistochemistry. We predict that stimulating the LPO increases the activity of dopamine neurons in the VTA and seeking behavior. This occurs via a GABAergic LPO-VTA pathway. Specifically, the LPO sends inhibitory GABAergic projections to the VTA. These synapse onto GABA neurons of the VTA resulting in dis-inhibition (i.e. excitation) of dopamine neurons. We expect these studies to establish a novel role for the LPO as a key modulator of VTA neuron activity and cocaine seeking behavior. This provides a significant advancement in understanding circuits and mechanisms of addiction. In addition, these studies will advance our understanding of the brain, by discovering a role of a structure whose function is largely unknown.